This invention relates to selective application of liquid herbicides to crops and more particularly to farm implements for contact application of herbicides.
Many systems have been devised for applying liquid herbicides to weeds growing among crops. Aside from aerial spraying, most of these systems employ a spray boom or contact applicator boom designed for mounting on the front or back of a conventional farming tractor. Some of them also use wheels to support the ends of the boom with the implement being drawn in a trailer fashion behind the tractor. The wheels used on all of these herbicide applicators are heavy standard farming implement wheels. As is customary with farming implements, all of these devices are relatively heavy and generally are sized so as to require a conventional farming tractor or similarly-sized vehicle to support or pull the implement.
Contact herbicide applicators have come to be preferred over spray applicators, because in many situations they are more economical in their use of herbicide. However, contact applicators have heretofore been complicated, expensive implements. Also, prior contact applicators have been unreliable in their operation, particularly in uneven terrain, resulting in spotty herbicide application and wastage of contact herbicide liquid, which is very expensive.
For example, U.S. Pat. No. 4,208,835 by Roll et al. describes a self-propelled herbicide applicator mounted on a special purpose vehicle, e.g., a converted swather, using standard large-size farm implement wheels. Herbicide is applied to the growing weeds via a front-mounted roller which receives herbicide from a resilient belting wiper under which the roller turns. The applicator bar is raised or lowered hydraulically through actuator controls located in the tractor cab. Such a device is expensive due to the elaborate controls and the use of a dedicated special purpose vehicle. It is also very heavy therefore requiring large wheels which trample the crops.
Similarly, U.S. Pat. No. 4,223,478 by McHugh describes a heavy, three-point hitch-drawn herbicide applicator requiring support from large standard farming implement wheels and a standard farming tractor to pull the device. Herbicide is applied to the crops in a similar manner to Roll, et al. through a roller which rotates under a dispensing conduit which supplies herbicide to the roller.
Besides trampling the crops, the roller type contact applicators tend to waste herbicide. In an attempt to overcome that drawback, elaborate failure-prone herbicide-dispensing control systems have been proposed, as in U.S. Pat. No. 4,265,048 to Schepers, et al.
Not all contact herbicide applicators utilize a roller. Another well-known type of applicator uses a fixed hollow pipe as a wiper bar. One such design is that of U.S. Pat. No. 4,019,278 to McKirdy, which uses two parallel medium-diameter pipes. The pipes are perforated along the bottom and include a wick-like material which is soaked by liquid herbicide supplied to the pipe from a tank. A valve is provided at the base of the tank to control the rate at which herbicide trickles into the pipe in an attempt to limit wastage of the herbicide.
A second such design uses a comparatively wide diameter, hollow pipe which serves as both the reservoir for the liquid herbicide and the dispensing conduit. An example of this type of contact applicator is available from Rear's Manufacturing Company of Eugene, Oreg. It uses a three or four inch diameter pipe. Herbicide liquid is discharged through a multitude of holes in the bottom of the pipe. Segments of nylon rope are plugged into the holes to act as wicks in drawing liquid to the pipe surface. As the pipe is swept over the crops, contact of the ropes with the growing weeds transfers the herbicide and kills the weeds.
The hollow-pipe type of applicator is disadvantageous because it is difficult to control the discharge of liquid, particularly in uneven terrain. As the implement of the McKirdy patent is pulled downhill in sloped terrain, an adequate flow of liquid herbicide will not be drawn to the surface of the applicator bar. In both the McKirdy and Rear's devices, when the applicator is pulled along a side of a hill, the herbicide liquid flows in the pipe to one lateral side of the implement. This depletes the supply of liquid in the uphill end of the pipe and pools it in the downhill end, causing uneven application and herbicide wastage. Also, both devices require a farm tractor to pull them, which causes trampling of crops.
Hand tools for lawn and garden contact herbicide application are known which utilize a system for drip feeding liquid to a wiper head at the lower end of the tool. For example, U.S. Pat. Nos. 4,305,224 and 4,357,779 to Maddock describe a hand-held liquid herbicide applicator which drip-feeds herbicide liquid from a reservoir in the tool handle to a wicking element, such as a sponge, partially enclosing the underside of a tubular dispensor conduit. A plurality of apertures are provided along the underside of the conduit for feeding liquid to the sponge. Herbicide flow to the sponge is maintained through a drip-feed control valve to assure an adequate yet not abundant flow to the sponge. Such a configuration would not prove useful in the above described applicator implement as the same problem of an inadequate herbicide distribution over sloped terrain would still be present. Similarly, Maddock does not suggest how to utilize his applicator head in a farm implement.
Therefore, a need exists for a new and improved farm implement for contact application of liquid herbicide, which will not trample crops and which provides effective control of liquid herbicide flow rates to a wiper bar regardless of the slope of the terrain over which the implement is used.